Satellite-enabled node for ambient noise tomography

ABSTRACT

Embodiments relate to data acquisition units or nodes and more specifically to seismic data acquisition units or nodes for use in data gathering for ambient noise tomography (ANT). Some embodiments relate to a method for data acquisition, and systems employing one or more data acquisition units. Some embodiments relate to systems comprising one or more satellites in communication with one or more data acquisition units for communication to a remote server, for remote storage, and processing for creating sub-surface tomography images accessible to client devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(a) to Australianpatent application No. 2022209325, filed Jul. 28, 2022; claims priorityunder 35 U.S.C. § 119(a) to Australian patent application No.2022900680, filed Mar. 18, 2022; and claims priority under 35 U.S.C. §119(a) to Australian patent application No. 2022900533, filed Mar. 4,2022, each of which are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

Embodiments relate to data acquisition units or nodes and morespecifically to seismic data acquisition units or nodes for use in datagathering for ambient noise tomography (ANT). Some embodiments relate toa method for data acquisition, and systems employing one or more dataacquisition units. Some embodiments relate to systems comprising one ormore satellites in communication with one or more data acquisition unitsfor communication to a remote server, for remote storage, and processingfor creating sub-surface tomography images accessible to client devices.

BACKGROUND

Data acquisition for ambient noise tomography processing can be a timeconsuming endeavour. Ambient noise tomography requires continuoussampling. There may be significant latency from deploying dataacquisition sensors and subsequently collecting the data measured fromthe data acquisition sensors to producing ambient noise tomographyimages, which can take from several weeks to several months.Furthermore, the data acquisition sensors for ambient noise tomographymay need to be deployed in remote and/or harsh environments which canpresent various challenges. In remote and harsh environments without apower supply, there may be data storage and power constraints associatedwith data acquisition for ambient noise tomography.

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is not to betaken as an admission that any or all of these matters form part of theprior art base or were common general knowledge in the field relevant tothe present disclosure as it existed before the priority date of each ofthe appended claims.

SUMMARY

Some embodiments relate to a data acquisition unit, including:

-   -   a housing;    -   a ground movement data acquisition mechanism configured to        measure ground movement;    -   a processing unit communicatively coupled to the ground movement        data acquisition mechanism,    -   wherein the processing unit is configured to receive ground        movement data sent from ground movement data acquisition        mechanism, the processing unit further configured to pre-process        the ground movement data before transmitting, via a satellite        modem, to a communicatively coupled LEO satellite the        pre-processed data based on a scheduled timing of the LEO        satellite reaching a scheduled orbital position.

The ground movement data acquisition mechanism and processing unit maycontinuously acquire and preprocess ground movement data and transmitall or almost all the pre-processed data to a remote server system viathe low earth orbit satellite for performing ANT.

Pre-processing the ground movement data may include one-bitnormalisation.

Pre-processing the ground movement data may further include de-trendingthe ground movement data. Pre-processing the ground movement data mayfurther include low-pass filtering. Pre-processing the ground movementdata may further includes decimating by a pre-determined factor thatdepends on a sampling rate. The factor may be two where the samplingrate is 25 Hz, for example. Pre-processing the ground movement data mayfurther includes spectral whitening. The de-trending may be performedfirst, followed by decimating by a pre-determined factor, followed bylow-pass filtering, followed by spectral whitening, followed by one-bitnormalisation.

Some embodiments relate to a data acquisition unit for ambient noisetomography (ANT), including:

-   -   a closed housing including a top portion, a central portion and        a lower portion, the lower portion including a vibration sensing        portion for sensing vibration in a ground region;    -   a vibration transducer in the housing and configured to receive        vibrations via the vibration sensing portion and generate an        electrical output signal based on the received vibrations:    -   a processing unit in the housing to receive and process the        electrical output signal to generate a compressed data payload;    -   a synchronisation unit to receive a synchronisation signal from        a satellite and to communicate synchronisation data to the        processing unit based on the synchronisation signal;    -   a satellite modem communication port positioned on top of the        top portion for allowing communication between a satellite modem        and the processing unit to transmit the data payload to a low        earth orbit satellite; and    -   a power supply in the central portion to supply power to the        processing unit, the satellite modem and the synchronisation        unit.

The vibration transducer may include a geophone positioned in thevibration sensing unit. The vibration sensing unit may include a metalspike or probe having one end received in the lower portion and a freeopposite end for extending into part of the ground region. The powersupply or power source may consist of a rechargeable battery modulecentrally positioned within the housing. The processing unit orprocessor may be disposed between the power supply or power source andthe ground movement sensing module, sensing probe, vibration transduceror the vibration sensing portion.

The unit may further include a low-power wide-area network (LPWAN)antenna connection jack in a top portion of the housing for coupling aLPWAN antenna to the processing unit.

The processing unit or processor may be configured to buffer payloaddata for a pre-determined period of time less than 12 hours. Thesatellite modem may be configured to transmit the data payload to aremote server in near-real time.

The processing unit or processor may send the data payload at arandomised time within a scheduled transmission period. The randomisedtime may be based on a unique key. The unique key may be a hardwareserial number of the satellite modem.

The data acquisition unit may further include an inertial measurementunit for measuring an attitude and/or orientation of the dataacquisition unit, wherein the processing unit or processor batches theattitude and/or orientation data in a payload for transmission so thatthe attitude and/or orientation, or a change of attitude and/ororientation, of the data acquisition unit, can be visualised on oralarmed to a user device.

The data acquisition unit may further include a removable auxiliarymemory for storing the data payload for data recovery or re-transmissionof one or more of the data payloads upon communication and/or componentfailure.

Some embodiments relate to a method of seismic data acquisition,including:

-   -   positioning a plurality of data acquisition units according to        any one of the described data acquisition unit embodiments at        spaced surface locations across a ground region; and    -   operating each of the plurality of data acquisition units to        receive vibrations over a plurality of days;    -   wherein the plurality of data acquisition units are operable to        generate and send to a satellite processed data based on        vibrations received by the data acquisition units at the spaced        surface locations.

The operating may include continuous operation of the data acquisitionunits to receive vibrations. The operating may include continuousoperation of the data acquisition units to receive vibrations for aperiod of between 4 and 10 days. A power supply or power source of eachdata acquisition unit may be contained within the housing of each dataacquisition unit and may be configured to supply power for operation ofthe respective data acquisition unit for up to 10 days. In someembodiments, the power supply or power source of each data acquisitionunit may be configured to supply power for operation of the respectivedata acquisition unit for up to 10 days. In some embodiments, the powersupply or power source of each data acquisition unit may be configuredto supply power for operation of the respective data acquisition unitfor greater than 10 days.

Some embodiments relate to a server system, including: a datacommunications module for receiving from a plurality of data acquisitionunits pre-processed ground movement data based on ground movement in aground region sensed by each of the plurality of data acquisition units;a data processing module for performing ambient noise tomography togenerate tomography data based on the ground-movement data; and a datavisualisation module for generating a display of the ground region basedon the tomography data viewable from a communicatively coupled userinterface in near-real time relative to a data acquisition time of theground movement.

The pre-processed ground movement data may be received from the dataacquisition unit via communications of a low earth orbit satellite.

Also disclosed herein is a data acquisition unit or node for ambientnoise tomography (ANT), including:

-   -   a closed housing including a top portion, a central portion and        a lower portion, the lower portion including a vibration sensing        portion for sensing vibration in a ground region;    -   a vibration transducer in the housing and configured to receive        vibrations via the vibration sensing portion and generate an        electrical output signal based on the received vibrations:    -   a processing unit in the housing to receive and process the        electrical output signal to generate a compressed data payload;    -   a synchronisation unit to receive a synchronisation signal from        a satellite and to communicate synchronisation data to the        processing unit based on the synchronisation signal;    -   a satellite modem positioned on top of the top portion and in        communication with the processing unit to transmit the        compressed data payload to a satellite; and    -   a power supply in the central portion to supply power to the        processing unit, the satellite modem and the synchronisation        unit.

Also disclosed herein is a data acquisition unit including:

-   -   a housing;    -   a ground movement sensing module, the ground movement sensing        module either contained in the housing or coupled to the        housing;    -   a processing unit contained in the housing, the processing unit        being communicatively coupled to the ground movement sensing        module to receive ground movement data from the ground movement        sensing module, the processing unit further configured to        preprocess the ground movement data before transmitting the        preprocessed data to a satellite modem for transmission to a low        earth orbit (LEO) satellite;    -   wherein preprocessing the ground movement data comprises at        least 8:1 up to 32:1 compression ratio of the ground movement        data. In other words, preprocessing the ground movement data        comprises compressing the ground movement data at a compression        ratio of at least 8:1 up to 32:1.

Also disclosed herein is a data acquisition unit, including:

-   -   a housing;    -   a ground movement data acquisition mechanism;    -   a processing unit communicatively coupled to the ground movement        data acquisition mechanism, the processing unit configured to        receive ground movement data measured and sent by the ground        movement data acquisition mechanism, the processing unit further        configured to pre-process the ground movement data before        transmitting the pre-processed data;    -   wherein pre-processing the ground movement data includes one-bit        normalisation.

Also disclosed herein is a data acquisition unit, including:

-   -   a housing including an outer wall, a top part and a bottom part,        wherein the outer wall, the top part and the bottom part        together define an interior volume of the housing;    -   a sensing probe extending from the bottom part of the housing;    -   a first printed circuit board assembly (PCBA) located above the        sensing probe, the first PCBA contained in the housing;    -   a processor included on the first PCBA;    -   a global navigation satellite system (GNSS) module included on        the first PCBA for processing a time synchronisation signal;    -   a power source located above the first PCBA, the power source        contained in the housing;    -   a second PCBA located above the power source, the second PCBA        contained in the housing;    -   wherein the top part allows a satellite communications module to        be attached to the data acquisition unit, and the second PCBA        permits communicative coupling between the processor and the        satellite communications module.

Also disclosed herein is a server system, including:

-   -   a data communications module for receiving pre-processed ground        movement data based on ground movement in a ground region sensed        by each of a plurality of data acquisition units via a        satellite;    -   a data processing module for performing ambient noise tomography        to generate tomography data based on the ground-movement data;        and    -   a data visualisation module for generating a display of the        ground region based on the tomography data viewable from a        communicatively coupled user interface in near-real time        relative to a data acquisition time of the ground movement.

Also disclosed herein is a system including the server system and one ormultiple ones of the data acquisition unit as described herein.

Also disclosed herein is a method performed on a server system,including:

-   -   receiving pre-processed ground movement data based on ground        movement in a ground region from each of a plurality of data        acquisition units resting on the ground region via a satellite;    -   performing ambient noise tomography to generate tomography data        based on the ground-movement data; and    -   generating a display of the ground region based on the        tomography data viewable from a communicatively coupled user        interface in near-real time relative to a data acquisition time        of the ground movement.

The data acquisition unit may include a communications unit and/or asatellite modem for transmitting the pre-processed data.

The processing unit may generate and store payloads containing thepre-processed ground movement data, before forwarding, at apre-determined time, the pre-processed ground movement data to thecommunications unit or satellite modem for transmission.

The processing unit may generate and forward payloads containing thepre-processed ground movement data to the communications unit orsatellite modem for transmission.

The data acquisition unit may include the communications module fortransmitting the pre-processed data to at least one user device, basestation, network node, and/or gateway device which may be in a vehicle,carried by a user, or statically deployed.

Also disclosed herein is a system including the server system and one ormultiple ones of the data acquisition unit as described herein.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a remote backhaul system 100 according tosome embodiments.

FIGS. 2A and 2B show external isometric views of data acquisition unitaccording to some embodiments.

FIG. 3 shows a cross-sectional view of data acquisition unit accordingto some embodiments.

FIG. 4 shows a cross-sectional view of data acquisition unit from aboveaccording to some embodiments.

FIG. 5 shows a cross-sectional view of a bottom part of the dataacquisition unit according to some embodiments.

FIGS. 6A and 6B show external views of the upper part of dataacquisition unit according to some embodiments.

FIGS. 6C and 6D show cross-sectional views of the upper part of dataacquisition unit according to some embodiments.

FIG. 7 shows components of the data acquisition unit according to someembodiments.

FIGS. 8A and 8B show the printed circuit boards of the data acquisitionunit according to some embodiments.

FIG. 9 is an example block diagram of a data acquisition unit accordingto some embodiments.

FIG. 10 shows a flow diagram of a method of sampling by data acquisitionunit according to some embodiments.

FIG. 11 shows a flow diagram of a method of sampling by data acquisitionunit according to some other embodiments.

FIG. 12 shows a flow diagram of a method of pre-processing of thesampled data by the processor of data acquisition unit according to someembodiments.

FIG. 13 shows a flow diagram of a method of sampling and pre-processingby the data acquisition unit according to some embodiments.

FIG. 14 shows a schematic diagram of electronic components of the dataacquisition unit according to some embodiments.

FIGS. 15A, 15B, and 15C show sub-surface imaging according to someembodiments.

FIG. 16 shows sub-surface imaging according to some embodiments.

FIG. 17 shows a flow diagram of a method of sampling by data acquisitionunit according to some other embodiments.

FIGS. 18A and 18B show external isometric views of data acquisition unitaccording to some other embodiments.

FIGS. 19A and 19B show the printed circuit boards of the dataacquisition unit according to some other embodiments.

FIGS. 20A and 20B show a schematic diagram of electronic components ofthe data acquisition unit according to some other embodiments.

FIG. 21 shows a cross-sectional view of data acquisition unit from aboveaccording to some other embodiments.

FIG. 22 shows a cross-sectional view of the bottom part of the dataacquisition unit according to some other embodiments.

DETAILED DESCRIPTION

Embodiments relate to data acquisition units and more specifically toseismic data acquisition units for use in ambient noise tomography(ANT). Some embodiments relate to a method for data acquisition, andsystems employing one or more data acquisition units. Some embodimentsrelate to systems comprising one or more satellites in communicationwith one or more data acquisition units for communication to a remoteserver, for remote storage and processing for creating sub-surfacetomography images accessible to client devices. The sub-surfacetomography images may be ambient noise tomography images created fromambient noise tomography processing.

According to some embodiments, the data acquisition units may be capableof direct radio communications with a low earth orbit (LEO) satellitenetwork. The data acquisition units may be capable acquiring groundmovement measurements, processing the measurement data, transmitting thedata via the LEO satellite network to be received by a server system forambient noise tomography processing in about 2 minutes to 2 hoursdepending on satellite availability, immediately after the dataacquisition unit is deployed. Thus, the embodiments allow near-real timereception of data from the data acquisition units, for example forambient noise tomography purposes. In this context of geological featureobservation (i.e. long time scale as opposed to high speed computing),near-real time is intended to include periods of as low as around 1-2minutes latency up to around 2-4 hours or 6-12 hours latency fromvibration sensing to reception at the remote server. This allows imagesto be formed at remote client computing devices from the ambient noisetomography within a matter of days, such as around 4 days, as thereceived data accumulates to provide a higher and higher resolutionimage.

As soon as a data acquisition unit is placed, the unit can be turned onand operated so that ambient noise tomography processing can commencewhilst other data acquisition units are added to the array of dataacquisition units for imaging a sub-surface region according to someembodiments. The imaging and the sub-surface region which is imaged maybe three dimensional (3D).

Ambient noise tomography images according to some embodiments may beavailable for viewing on a client device communicatively coupled to theserver system within 24 hours (for low resolution) and more substantial(higher resolution) images within 4 to 5 days. The resolution andinformation richness of the ambient noise tomography images may beiteratively improved upon subsequent sampling and transmission of datafrom the data acquisition units over the sampling period of 4 to 10 daysor 2 to 8 days, for example.

According to some embodiments the data acquisition units may beself-contained and include a ground sensing module, processor, memory, apower source, and an attachable satellite communications module. Thedata acquisition units may be able to operate and sample continuouslyand transmit the data for 5 to 10 days without any further (external)power source. In some embodiments, data acquisition units may samplecontinuously and transmit data for more than 10 days. For example, adata acquisition unit may sample continuously and transmit data forabout 5 to 11 days, 5 to 12 days, 5 to 13 days, 5 to 14 days, or 5 to 15days without any further (external) power source, for example. Thepower, storage, and transmission requirements of this operation may beaided by preprocessing the acquired data (to drastically compress thedata by 8:1 or 16:1 or 32:1, for example) from the ground sensingmodule. The power source may be or include a rechargeable battery pack,for example.

According to some embodiments, the data acquisition unit measuresseismic vibration in the ground region near where it is deployed. Ageophone element may be used to generate electrical signals proportionalto the vibrational velocity induced in the sensor. This signal isdigitised and stored in a data buffer. Ambient noise tomography usuallyrequires a continuous stream of data. In addition, only the z-axis(coaxial with the local gravity vector) may be required. The dataacquisition unit may sample its single geophone every 40 milliseconds(25 Hz), for example. It may store each sample in a software buffer.This sample rate could be higher, but as will become clear, the higherthe sample rate, the greater the processing capability (and non-volatilestorage) needs to be. The samples buffer may be able to hold 512samples, for example. In some other embodiments, the buffer size may be64, 128, 256, 512, or 1024 samples. Once the current buffer is full, thebuffer contents is passed down into a sequence of digital signalprocessing functions. Whilst this processing is happening (taking upcomputer resources), new samples obtained from the geophone are insertedinto a second buffer. As such, between these two buffers, one willalways be used for the processing algorithms and the other will be usedto receive new samples.

According to some embodiments, the digital signal pre-processingcomposes of six stages. The fundamental purpose of these pre-processingalgorithms is to condition the data for seismic analysis and reduce thedata size significantly. The first stage may optionally decimate thedata. The second stage de-trends or de-biases the data. This is intendedto remove inherent biases in the geophone signal (such as a DC bias ortemperature influence). The third pre-processing stage uses a fastFourier transform (FFT) algorithm to convert the time-domain seismicsignal into its frequency constituents. This FFT algorithm requires thedata buffer size to be an exponent factor of two. With the data in thefrequency domain, the signal can be filtered by applying pre-determinedfilter coefficients or making changes to the amplitude and frequencybins. The fourth pre-processing stage spectrally whitens the filtereddata. By whitening the data, the amplitude across a frequency range canbe essentially normalised with a Tukey window. The rounded edges areintended to reduce any aliasing (artefacts) when transforming thefiltered data back into the time domain. The fifth pre-processing stagedoes this transformation by using the inverse fast Fourier transform(IFFT) algorithm. The sixth and final pre-processing stage of thisprocessing pipeline includes one-bit normalising the data. With one-bitnormalising, amplitudes that are positive are represented with a one,and conversely amplitudes that are negative are represented with a zero.Even though the amplitude information of the original seismic signal isessentially obliterated, the phase information of the signal ispreserved. The phase information may be more helpful or essential thanthe amplitude information for processing ambient noise tomography at theserver system where the data is used to generate three-dimensionalsubsurface models.

The one-bit normalisation may compress the data substantially, allowingthe original four-byte sample (from a 32-bit analogue to digitalconverter) to be represented by a single bit (e.g. 32:1 compressionratio). From the perspective of a payload that can be sent from the dataacquisition unit via the satellite modem, each byte will contain eightsamples. In other embodiments, a lesser compression ratio, such as 8:1or a compression ratio between 8:1 and 32:1, may be used.

The housing may be secured into the ground and radial buttresses or ribsmay project from an underside of the housing (e.g., extending betweenthe outer wall and an upper part of the sensor probe housing part) tomitigate or resist rotation of the housing or the sensing probe. Thehousing may have two printed circuit boards (PCBs), each mountingcomponents of the data acquisition unit to form respective printedcircuit board assemblies (PCBAs), to improve the configuration ofcabling within the housing. The housing may have panels on side faces ofan upper part of the housing situated to be located above an earthsurface when the data acquisition unit is deployed in the earth, toimprove the amount of surface area to be utilised for externalfacing/protruding components of the data acquisition unit. The panelsmay be flat to host components such as receptacles, buttons andantennas, and may form a hexagonal shape to better tessellate to panelsof other data acquisition units for easy packing and charging on acharging rack. In some embodiments, at least one of the data acquisitionunits may be placed in a charging case for charging. The charging casecan be used for transporting the at least one of the data acquisitionunits to or from a site before, between, or after deployments. Transportcan be by a vehicle, such as a ground, air, or aquatic based transportvehicle.

FIG. 1 is a block diagram of a sub-surface tomography system 100according to some embodiments. The sub-surface tomography system 100 mayalso be described as a data acquisition system 100. The sub-surfacetomography system 100 comprises a data acquisition unit array 115. Thedata acquisition array 115 comprises one or more data acquisition units110. The data acquisition unit 110 may also be referred to as a seismicdata acquisition unit, vibration sensing apparatus, seismometer module,geophone apparatus, geologic instrument, data acquisition node,end-node, node device or a sensor node. The data acquisition unit 110may also be referred to as “smart seismometer”.

The data acquisition unit 110 may be capable of wireless communicationbetween the seismic data acquisition unit 110 and a user device. Thewireless communication between the data acquisition unit 110 and theuser device may be a LPWAN communication link. For example, thecommunication link may be in the form of a LoRaWAN wireless link or aNarrowband Internet of Things wireless link or Sigfox LPWAN wirelesslink or any other wireless communication link suitable for a low-powerwide-area network communication. Communication over the wirelesscommunication link may be made resilient to interference by utilisingspread spectrum techniques, such as Direct Sequence Spread Spectrum(DSSS) or Chirp Spread Spectrum (CSS), Random Phase Multiple Access(RPMA) and Listen-Before-Talk (LBT), for example. In such communication,the wireless device may act as a beacon to assist a user of the userdevice to locate the data acquisition unit 110. The data acquisitionunit 110 may also communicate to the wireless device diagnosticinformation, such as whether the data acquisition unit has low batterylevels, for example. The wireless communication between the dataacquisition unit 110 and the user device 160 may also comprise or beperformed using other protocols, such as Bluetooth Low Energy (BLE), forexample.

In some embodiments, the data acquisition unit 110 comprises LPWANantennas that are configured to communicate over 8 or 16 radio channels.The data acquisition unit 110 may communicate with a user device withina range of 20 km, for example. The LPWAN antenna of the data acquisitionunit 110 may be configured to communicate using the LoRa™ technologyover the frequency bands 902-928 MHz, 863-870 MHz, 433-434 MHz, forexample. The data acquisition units 110 may also be configured tocommunicate over Bluetooth (or other short-range) technology or overWiFi™ with devices located in its immediate vicinity, for example withina range of 15 m. In some other embodiments, at least some of the dataacquisition units 110 may be configured to communicate via radio/mobileprotocols defined by 3GPP, according to 3G, 4G, or 5G standards, forexample. This may be helpful for implementations of sub-surfacetomography system 100 using vehicular based network nodes for mobilebackhaul to server system, instead of satellite communications, forexample.

The sub-surface tomography system 100 also comprises a satelliteconstellation 135. The satellite constellation 135 comprises one or moresatellites 130. Each of the one or more satellites 130 may be a LowEarth Orbit (LEO) satellite 130. In some other embodiments, one or moreof satellites 130 may be a Geostationary (GEO) satellite 130. Thesatellite 130 is capable of communicating with data acquisition unit 110over a communication link 118. In embodiments with more than onesatellite 130, the communication link 118 may extend to the more thanone satellite 130. The communication link 118 may not be a persistentcommunication link and if satellite 130 is not accessible to the dataacquisition unit 110, the data acquisition unit 120 may await theresumption of the radio communication link 118 to continue communicationof information.

Radio communication links 118 are radio links to satellites 130 orbitingthe earth to communicate data acquired from the one or more dataacquisition units 110 of the data acquisition array 115 and receiveinstructions or configuration information or firmware updates for theone or more seismic data acquisition units 110.

The sub-surface tomography system 100 also comprises one or more groundstations 140. The ground stations 140 receive communication from one ormore satellites 130 of the satellite constellation 135 over acommunication link 138. The communication link 138 may be facilitated byradio waves of suitable frequency according to the region where theground station 140 is located.

The satellite 130 may be a LEO satellite that circles the earthapproximately every 90-110 minutes, for example. With such orbitingsatellites, a relatively smaller number of satellite ground stations 140may be used to receive downlinks from satellite 130, or all the datatransmitted by the one or more data acquisition units 110 of the dataacquisition array 115.

In some embodiments, satellites 130 in a near polar orbit may be usedand ground stations 140 may be located near each of the Earth's poles.This arrangement allows each satellite 130 to connect to a groundstation 140 on almost every orbit, leaving the throughput latency nohigher than around 45 minutes (half the time required to complete anorbit), for example. In some embodiments, ground stations may be locatedat lower latitudes with less harsh weather and transport, and easieraccess to power and communication links to the ground station 140. Theground station 140 may comprise radio communication equipment necessaryto communicate with the satellite 130 and a communication interface torelay received information to a server system 150 over a communicationslink 148. The communication link 148 may be a wired or wirelesscommunication link to the internet available to the ground station 140and to the server system 150. The server system 150 may be accessibleover the internet through an application or platform on a client device160 over a conventional internet connection over the communication link157. The communications of server system 150 may be handled by a serversystem communications module. The client device 160 may be an end usercomputing device such as a desktop, laptop, mobile device, tablet, forexample.

The server system 150 may be configured to decode, decrypt and/ordecompress communications originating from the data acquisition units110 and received over the communication links 118, 138 and 148 and storeany data from the communications in data storage 152. In some otherembodiments, the server system 150 may receive communicationsoriginating from the data acquisition units 110 and store any data fromthe communications in data storage 152.

In some embodiments, server system 150 may further comprise a tomographymodule 154 (which includes program code) executable by a processor ofthe server system 150 or the tomography module 154 may be locatedseparately and communicatively coupled to the server system 150 via link153. Tomography module 154 may also be referred to as subsurface imagingmodule 154, or ambient noise tomography (ANT) module 154, for example.When executed, tomography module 154 may read data from thecommunications originating from the data acquisition units stored indata storage 152. The tomography module 154 may perform sub-surfacetomography processing using the read data from the data storage 152. Thesub-surface tomography processing may comprise ambient noise tomographyprocessing. After performing sub-surface tomography processing, thetomography module 154 may send the sub-surface tomography data via link153 to be stored in data storage 152. Sub-surface tomography data may bedata that can be processed to generate one or more sub-surfacetomography images. Sub-surface tomography data may be data that can beprocessed to generate one or more sub-surface tomography images, such asone or more 3-D sub-surface tomography images.

Server system 150 may comprise or have access to code for executing adata visualisation module 156. The data visualisation module 156 may bea platform accessible to client device 160. The data visualisationmodule 156 may read sub-surface tomography data from the data storage152. The data visualisation module 156 and/or client device 160 mayprocess sub-surface tomography data to generate sub-surface tomographyimages to be viewed on client device 160. The generated sub-surfacetomography images may be ambient noise tomography images.

The sub-surface tomography system 100 enables high-latency communicationof data between the data acquisition array 115 and the client device160. High-latency communication may be inherently suitable fortransmitting small messages to and from the data acquisition array 115deployed in remote locations and the server system 150. High-latencycommunication may comprise latency of greater than about 1 second, 2seconds, 15 seconds, 30 seconds, or 1, 2, 3, 4 or 5 minutes, forexample. Two high-latency communication methods are store and forwardcommunication and short burst data communication.

Store and forward communication may be implemented by the satelliteconstellation 135 that periodically passes into a range wherecommunication may be received from the data acquisition units 110positioned in a remote location. Satellite 130 may gather data from thedata acquisition units 110 and deliver it back to ground stations 140that are connected to a network backbone or a network generallyaccessible over the internet. In some embodiments, the store and forwardcommunication could be implemented by satellites or any type of air,ground or sea vehicles (carrying suitable communication and storageequipment) that intermittently travel within communications range of thegateway device 120 or data acquisition unit 110. For example,alternative implementations to satellite based store and forward mayinclude wireless communications between the data acquisition units 110with one or more user device, base station, network node, and/orgateways. The one or more user device, base station, network node,and/or gateways may be vehicle mounted, for example in an automobile orin an aerial vehicle such as an unmanned aerial vehicle (UAV) or drone.The vehicle for vehicle mounting may be mobile piloted,semi-autonomously controlled, or autonomously controlled. At least oneuser device, base station, network node, and/or gateway device may becarried by a user/field operator whilst on foot or in a vehicle. In someembodiments, store and forward communications can be enabled via acommunications handshake between satellite modem, processor, and/or acommunications unit of data acquisition unit 110 and at least one userdevice, base station, network node, and/or gateway device. The transfersof data by the store and forward method may be bi-directional. Thevehicles or satellites used to implement store and forward communicationcan be far less numerous than a number of statically deployedterrestrial devices that would be needed to cover a designated remotearea. Further, vehicles or satellites used to implement store andforward communication can be more rapidly deployed, which can save timeduring the implementation of the sub-surface tomography system 100,reduce the duration of blackouts resulting from failure of staticallydeployed terrestrial devices and permit maintenance operations andsystem upgrades to be carried out using the server system 150 ratherthan on site in the field.

In some other embodiments, data acquisition units 110 are incommunication with and/or within wireless communication range of atleast one user device, base station, network node, and/or gateway devicewhich is stationary. The at least one stationary user device, basestation, network node, and/or gateway device may be statically deployed.Data acquisition units 110 may store and forward or transmit sampleddata by other means to the at least one stationary user device, basestation, network node, and/or gateway device. At least one stationaryuser device, base station, network node, and/or gateway device may havea satellite modem to communicate with satellite constellation 135, ormay have another backhaul method available such as mobile and/or opticalbackhaul, for example.

Short Burst Data (SBD) is another technique for communicating short datamessages between seismic data acquisition unit 110 and a centralisedhost computing system such as the server system 150. SBD satellitemessaging systems work by waiting for a suitable slot in a satellitenetwork that has voice as its primary application. Examples includeOrbcomm™, Iridium™ and Globalstar™. The voice traffic in such systems isprioritised and requires latencies typically less than 500 ms, forexample. However, due to the fluctuating demands for voice traffic,there are windows in which shorter messages can be sent. This isanalogous to the Short Messaging System (SMS) technique/standard used interrestrial communications networks design for mobile telephony. Thetypical latencies of the SBD traffic in such systems can be in the rangeof 5 seconds to 10 minutes or greater, for example.

FIGS. 2A and 2B show external views of seismic data acquisition unit 110according to some embodiments. The data acquisition unit 110 maycomprise a data acquisition device 213 in combination with a satellitemodem 220, as also shown in FIG. 3 . The data acquisition device 213 maycomprise closed housing 205. Closed housing 205 may comprise an upperpart 210 and a bottom part 230. The upper part 210 and the bottom part230 are configured to mate and seal with each other (with suitablesealing material) to form a substantially closed and sealed internalchamber. The seal may prevent soil and/or moisture such as water,ingress into the chamber. Upper part 210 may be formed of aluminum oranother light but strong metal or material, for example. Bottom part 230may be formed of aluminum or another light but strong metal or material,for example. Bottom part 230 may comprise a vibration sensing portion250, removably or irremovably coupled to and/or extending from thebottom part 230. Vibration sensing portion 250 may be referred to assensing probe 250 or spike 250. Vibration sensing portion 250 includes anarrowing (generally conical) distal tip 251 at a lower extremity of thevibration sensing portion 250.

Vibration sensing portion 250 may be formed of stainless steel oranother suitably hard metal for effectively transmitting externallyoriginating vibrations to a vibration transducer housed in and/or inmechanical communication with the sensing portion 250.

Vibration sensing portion 250 may comprise one or more probe recesses252. The one or more probe recesses 252 may be shaped to provide asurface to engage with a tool, such as a spanner, to assist couplingvibration sensing portion 250 to an underside surface of bottom part230. In some other embodiments, as shown in FIG. 22 , vibration sensingportion 250 does not include one or more probe recess 252. In some otherembodiments, as shown in FIG. 22 , vibration sensing portion 250includes an engagement projection 2250 around the vibration sensingportion 250. Engagement projection 2250 may engage with a tool, such asa spanner to assist coupling vibration sensing portion 250 to anunderside surface of bottom part 230. The engagement projection 2250 mayhave engagement lands, such as flat faces, for example in theapproximate shape of a hexagon or square. The engagement projection 2250may be located proximate to the bottom part 230. In such embodiments,the sensing portion 250 is provided with a more uniformly taperingcross-section between the mid-section of the sensing portion 250 and thedistal tip 251. This provides improved penetrability and strength ofsensing portion 250.

Upper part 210 may comprise a top surface 217. Top surface 217 may be anexterior surface of the upper part 210.

Upper part 210 may comprise a side circumference as long or longer thanthe side circumference of bottom part 230. Upper part 210 may compriseflat side panels 211. Flat side panels may be connected around the sidesof the upper part 210 to form a hexagonal shape. The hexagonal shape ofthe upper part 210 may be useful for tessellating the data acquisitiondevice 213 with other data acquisition devices 213 when transporting orcharging together, when on a charging rack for example. In someembodiments, the data acquisition units 110 may be placed in a chargingcase for charging. The charging case can be used to transport the dataacquisition units 110 in the field and for road/air freight.

Data acquisition device 213 may comprise a power switch 214. The powerswitch 214 may be located on a side panel 211. The power switch 214 maybe communicatively coupled to a power source, which powers the dataacquisition device 213. Power switch when actioned may allow dataacquisition device 213 to be activated without the need to open ordisassemble data acquisition device 213.

Data acquisition device 213 may comprise a passive global navigationsatellite system (GNSS) antenna 262. Passive GNSS antenna 262 may extendfrom a side panel 211, for example. Passive GNSS antenna 262 may extendfrom a connection jack on side panel 211, for example. Passive GNSSantenna 262 may be connected to the data acquisition device 213 fromconnector 216. Passive GNSS antenna 262 may be assisted by an inbuiltlow noise gain (LNA) on a PCBA within the data acquisition device 213,for example. Passive GNSS antenna 262 may have less power consumptionthan an active antenna. Passive GNSS antenna 262 may be an antenna forreceiving global positioning system (GPS), GLONASS, Beidou, or Galileosignals, for example.

Data acquisition device 213 may comprise a communications antenna 266.Communications antenna 266 may extend from a side panel 211.Communications antenna 266 may extend from a connection jack on sidepanel 211. Communications antenna 266 may extend from a side panel 211which is not adjacent to the side panel 211 which the passive GNSSantenna extends from. Communications antenna 266 may be a WANcommunications antenna. Communications antenna 266 may be a LPWANcommunications antenna in some embodiments. The data acquisition device213 is intended to be installed or positioned in the ground so that theside panels 211 and the associated peripherals (e.g. antennas, ports,switches) are above a soil surface, while the rest of the housing 205below the side panels 211 is submerged in the soil.

Data acquisition device 213 may comprise an active GNSS antenna 264.Active GNSS antenna 264 may be coupled to the top surface 217. Topsurface 217 may have a recess to partially receive the active GNSSantenna 264. Active GNSS antenna 264 may be an antenna for receivingGPS, GLONASS, Beidou, or Galileo signals, for example. Data acquisitiondevice 213 may comprise a modem cap 220 as shown in FIG. 2 a . Modem cap220 may be an injection molded polymer.

Data acquisition unit 110 may include a satellite modem 290. Satellitemodem 290 may be referred to as satellite communications module 290.Satellite modem 290 may be a modem for communicating with one or moresatellites 130 from satellite constellation 135. Satellite modem 290 mayinclude an inbuilt-antenna. Satellite modem 290 may be an Orbcomm,Iridium, Fleet Space, Inmarsat, or Gilat modem, for example.

Modem cap 220 may shield the satellite modem 290 from weather or debris,for example. Modem cap 220 may shield the satellite modem 290 withoutaffecting or only slightly affecting the antenna performance of modem290.

Data acquisition device 213 may include a satellite modem receivingrecess 218, for receiving the satellite modem 290. The satellite modemreceiving recess 218 may be located on top surface 217. The satellitemodem receiving recess 218 may have screw holes or other attachmentfeatures for securing satellite modem 290 to the top of the dataacquisition device 213.

Data acquisition device 213 may also include one or more protectionplates 226. One or more protection plates 226 may also be referred to asmodem cable protection plate 226. The one or more protection plates 226may be configured to protect cables extending from a port of thesatellite modem 290 and/or the modem cap into a port or recess in topsurface 217 or a side panel 211. The one or more protection plates 226may prevent weather damage or tampering with the cables enclosed. Theone or more protection plates 226 may be positioned on or near a topedge portion of the upper part 210, as shown in FIGS. 2A and 2B.

Data acquisition device 213 may include a level indicator 280. Levelindicator 280 may be a spirit or bubble level indicator. Level indicator280 may be a bulls-eye indicator. Level indicator 280 may assist withorienting the data acquisition device 213 when deploying or physicallymanipulating the device, particularly for the alignment of vibrationtransducer 350 with local gravity vector.

Data acquisition device 213 may include a light emitting diode (LED)indicator 270. LED indicator 270 may illuminate, dim, and/or turn off toindicate warnings concerning battery level, for example. LED indicator270 may illuminate different colors such as green, amber, or red, forexample.

FIGS. 18A and 18B show perspective views of data acquisition unit 110according to some other embodiments.

According to some other embodiments, data acquisition unit 110 mayinclude a handle 1810 connectable to or through one or more portions ofthe top surface of upper part 217. In some embodiments, as shown inFIGS. 18A and 18B, handle 1810 is fed through two inlets on of upperpart 217. Handle ends 1812 of handle 1810 may be tied with respectiveknots to secure handle 1810 to data acquisition unit 110. Handle 1810may assist a user/field operator to carry data acquisition unit 110.Handle 1810 may assist a user/field operator to extract the dataacquisition unit 110 from the earth after deployment.

According to some other embodiments, data acquisition unit 110 may notinclude an active GNSS antenna 264, but instead include a passive GNSSantenna 262. According to some other embodiments, data acquisition unit110 may also include communications antenna 266.

FIG. 3 shows a cross-sectional view of data acquisition unit 110according to some embodiments.

The data acquisition device 213 may include a top portion 362, a centralportion 364, and a lower portion 366 as shown in FIG. 3 .

The top portion 362 may include a peripheral PCB 320. Peripheral PCB 320may also be referred to as PCBA 320. The peripheral PCB 320 may have oneor more ports to communicatively couple to a satellite modem 290. All ormuch of the upper part 210 may be included in the top portion 362.Satellite modem 290 may be positioned on top of the top portion 362.

The bottom portion 366 may include a vibration transducer 350. Vibrationtransducer 350 may also be referred to as geophone 350, ground movementsensing module 350, ground movement data acquisition mechanism 350, orground sensing module 350. The vibration transducer 350 may be in theclosed housing 205. The vibration transducer 350 may be in the closedhousing 205 by being received in the vibration sensing portion 250.

Vibration sensing module 350 may be or include a single geophone.Vibration sensing module 350 may be arranged to act as a vertical axisgeophone element. The geophone may have a natural frequency betweenabout 1 to 10 Hz. The geophone may have a natural frequency betweenabout 1 to 3 Hz, 1 to 5 Hz, or 2 to 8 Hz, for example. The geophone mayhave a natural frequency of about 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 3,3.5, 4, 4.5, 5, 6, 7, 8, 9, or 10 Hz for example. The geophone may havea sensitivity of about 100 to 300 V(m/s). The geophone may have asensitivity of about 180 to 260 V(m/s), 200 to 280 V(m/s), or 240 to 300V(m/s), for example. The geophone may have a sensitivity of about 120,140, 160, 180, 200, 220, 240, 260, 280, or 300 V(m/s), for example. Thegeophone may be Seis Tech ST-2A, for example.

The bottom portion 366 may include a PCB 310. PCB 310 may also bereferred to as PCBA 310, or Geologic Instrument PCBA 310. PCB 310 mayinclude a processing unit 902. The processing unit 902 may include aprocessor 984, non-volatile memory 930, and volatile memory 940 mountedthereon. PCB 310 may also include a global navigation satellite system(GNSS) unit 994. GNSS unit 994 may also be referred to as GNSS module994. PCB 310 may include an analogue to digital (ADC) converter 920 andan inertial measurement unit (IMU) 950. As shown in FIGS. 7 and 9 , PCB310 may be communicatively coupled to peripheral PCB 320.

The bottom portion 366 may include a probe gasket 352. Probe gasket 352may be formed of synthetic rubber, for example. Probe gasket 352 mayform a compressible blocking above the vibration transducer 350 andbelow a surface of the bottom part 230. The probe gasket 352 may beneoprene. The probe gasket 352 may be circular and/or annular. The probegasket 352 may be coupled to vibration transducer 350. The probe gasket352 may have a recess for allowing cabled connections from groundsensing module 350 to PCB 310 and/or processor 984 to communicativelycouple ground sensing module 350 to processor 984 and/or othercomponents on PCB 310, such as analog to digital converter 920 or memory940.

The bottom portion 366 may include a probe receiving recess 354. Probereceiving recess 354 may be a recess in bottom part 230 which is formedto receive a portion of sensing probe 250. The probe receiving recess354 and the portion of the sensing probe 250 which is received may eachinclude threads to threadedly engage with one another to secure sensingprobe 250 to bottom part 230.

The central portion 364 may include a power source 330 disposed in theinternal chamber defined by the upper part 210 and the bottom part 230.The data acquisition unit 110 may include a power supply. The powersupply may include power supply circuitry and/or connections on/tocomponents on PCBA 310 and/or PCBA 320. The power supply may includepower source 330. The power supply may supply power from power source330 to components of data acquisition unit 110 via circuitry and/orconnections to components on PCBA 310 and/or PCBA 320, such as processor984. The power supply may include a voltage/power regulator. Powersource 330 may also be referred to as power supply 330 or battery pack330. The power source 330 may be or include a battery pack. The powersource 330 may comprise one or more battery cells. The one or morebattery cells may be slightly smaller than double A, for example. Theone or more battery cells may be sized according to batteryidentification numbers 18650, 20700, 21700, or 38120, for example. Thepower source 330 may be or include at least one lithium ion (Li-Ion)battery, for example. The power source 330 is rechargeable via chargingport 630.

The central portion 364 may include or house one or more integrationcolumns 333. The one or more integration columns 333 may each beconnected in a respective column receiving recess 338 on the undersideof the upper part 210. The one or more integration columns 333 may bethreadedly engaged with their respective column receiving recesses 338.

Upper part 210 may comprise one or more integration columns 333. The oneor more integration columns 333 may extend from an underside of theupper part 210. The one or more integration columns 333 may be engagedto bottom part 230 to assist sealing the housing 205. The one or moreintegration columns 333 may be secured to bottom part 230 by one or morehousing screws 334. Each of the one or more housing screws 334 may bereceived through a respective underside portion or aperture (defined bya mounting portion 440) of the bottom part 230. The one or moreintegration columns 333 may be engaged to bottom part 230 to assistsealing the housing 205. Upper part 210 may comprise one, two, three,four, five, six, seven, or eight integration columns 333, for example.Upper part 210 may comprise four integration columns 333. Eachintegration column 333 may include one or more tool recesses 336 forengaging with a tool, such as a spanner, in order to fit (e.g. bythreaded engagement) each integration column 333 in a respective columnreceiving recess 338 on the underside of the upper part 210. Eachintegration column 333 and respective column receiving recess 338 mayhave threaded portions to engage with each other for fitting eachintegration column 333 in respective column receiving recess 338.

FIG. 4 shows a cross-sectional view of data acquisition unit 110 fromabove according to some embodiments while FIG. 5 shows a cross-sectionalview of the bottom part 230 of the data acquisition unit 110 accordingto some embodiments.

Bottom part 230 may comprise an internal floor 420 which faces theinterior of the housing 205, as shown in FIGS. 3, 4 and 5 . Bottomportion 366 may comprise internal floor 420 as shown in FIG. 3 .Internal floor 420 may have an inner upwardly expanding cone or frustumshape, outwardly bordered by a flat annular portion. The space definedby the inner cone or frustum shape of internal floor 420 may receive PCB310, as shown in FIG. 5 . PCB 310 may be round shaped or circular.

When printed circuit board 310 is received in the space defined by theinner cone or frustum shape of internal floor 420, there may be aremaining space or chamber underneath the printed circuit board 310 andbetween the printed circuit board 310 and the internal floor 420,synthetic rubber 352 and/or ground sensing module 350 as shown in FIGS.3 and 5 .

When printed circuit board 310 is received by the inner cone or frustumshape of internal floor 420, there may be space or chamber above theprinted circuit board 310 and between the printed circuit board 310 andthe power source 330 as shown in FIG. 3 .

Bottom part 230 may comprise an enclosed wall 430. Enclosed wall 430 maybe cylindrically shaped. Enclosed wall 430 may be connected to acircumference of internal floor 420. Enclosed wall 430 may be connectedto a circumference of the annular portion of the internal floor 420.

The bottom part 230 may comprise one or more column mounting portions440. Each of the one or more column mounting portions 440 may be locatedon a respective portion of the internal floor 420 of the bottom part230. The column mounting portions 440 may be shaped to receive both anintegration column 333 and a housing screw 334. Bottom part 230 maycomprise one, two, three, four, five, six, seven, or eight columnmounting portions 440, for example. Column mounting portions 440 mayeach comprise one or more circular or annular recess. Column mountingportions 440 may each comprise an O-ring. According to some otherembodiments, the integration columns 333 themselves may contain one ormore recess housing an O-ring at the column's 333 distal surface, whilecolumn mounting portion 440 may protrude from the underside of thebottom part 230 to engage with the one or more recess and O-ring. Theprotruding column mounting portion 440 can be seen in FIG. 22 .

Upper part 210 may comprise four integration columns 333, each columnhaving its own housing screw 334, column receiving recess 338, columnmounting point, and one or more tool recess 336.

Integration columns 333 may be cylindrically shaped. Integration columns333 may be cylindrically shaped and perforated with one or more toolrecess 336. Bottom part 230 may comprise or define one or more cablerecess 422 as shown in FIGS. 4 and 5 . Each of the one or more cablerecess 422 may be located on or defined by a respective portion of theinternal floor 420 of the bottom part 230. Cable recess 422 may be arecess which extends radially between a circumference of printed circuitboard 310 and a connection region between the internal floor 420 andinner wall 430. In some embodiments, bottom part 230 comprises 1 to 12cable recesses 422. In some embodiments, bottom part 230 comprises 2 to6, 4 to 10, or 6 to 12 cable recesses 422. In some embodiments, bottompart 230 comprises 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 cable recesses422. As shown in FIG. 4 , bottom part 230 may comprise 8 cable recesses422. Cable recesses 422 may guide and/or partially house cablesconnecting to printed circuit board 310, ground sensing unit 350, and/orcomponents on printed circuit board 310 to pass under and around powersource 330 to peripheral printed circuit board 320 and/or othercomponents or connectors of data acquisition unit 110.

Data acquisition device 213 may comprise one or more clamp structures433, as shown in FIGS. 4 and 5 . The one or more power clamp structures433 may be configured to hold power source 430 to bottom part 230 and tohold it securely within the housing 205. The one or more clampstructures 433 may be configured to hold power source 330 to theinternal floor 420 of bottom part 230. The one or more clamp structures433 may be coupled to and/or extend from internal floor 420 and/orbottom part 230. Data acquisition device 213 may comprise one, two,three, four, five, six or seven power clamp structures 433. In someembodiments, as shown in FIG. 4 , data acquisition device 213 comprisestwo clamp structures 433.

The one or more clamp structures 433 may comprise a power source clamp434. The power source clamp 434 may be an uppermost portion of a clampstructure 433. The power source clamp 434 may be configured to holdpower source 330 to bottom part 230. Power source clamp 434 may beadjusted vertically and/or rotated to permit the placement/removal ofpower source 330 and subsequent clamping of power source 430 to bottompart 230.

The one or more clamp structures 433 may also comprise a power sourcepositioning bracket 435. The power source positioning bracket 435 may bea bracket and/or structure with a recess which can receive power source330. The power source positioning bracket 435 may be shaped to receivepower source 330, for example. As shown in FIG. 4 , the power sourcepositioning bracket 435 may be shaped to receive a portion of a sideedge and portions of adjacent faces of a cuboid shaped power source 330.As shown in FIG. 4 , there may be two oppositely positioned clampstructures 433, each with a power source positioning bracket 435 whereinthe power source positioning brackets 435 receive opposite edges ofpower source 330. The two power source positioning brackets 435 mayserve to prevent power source 330 from moving when vibrations occur, forexample.

The one or more clamp structures 433 may also comprise one or more clampscrew recesses 436. The one or more clamp screw recesses 436 may providea recess for inserting one or more screws to secure power clampstructure 433 to internal floor 420 and/or bottom part 230. Power clampstructures 433 may comprise one, two, three or four clamp screwrecesses. In some embodiments, as shown in FIG. 4 , power clampstructure 433 may comprise two clamp screw recesses 436.

The one or more clamp structures 433 may also comprise one or more clamphole 437. Clamp hole 437 may be a recess which may receive a powersource clamp 434. Power source clamp 434 as shown in FIG. 5 is shown tobe already secured in a clamp hole, and another clamp hole 437 isvisible and unoccupied on the same power clamp structure 433. Powersource clamp 434 and clamp hole 437 may each include threads tothreadedly engage with one another.

FIGS. 21 and 22 show power clamp structure 433 according to some otherembodiments, wherein each power clamp structure 433 does not include abracket. In some other embodiments, the power clamp structures 433 canclamp a clamping sheet 2133 over power source 330, when power source 330is positioned within the housing 205. The clamping sheet 2133 may be ofa soft but durable material, such as a propylene diene monomer (EPDM),rubber, Neoprene, or polyethylene material, of suitable thickness andmass. The clamping sheet 2133 and power clamp structure are arranged soas not to put potentially damaging pressure on the top surface ormounting surfaces of the power source 330 and the printed circuit boardassembly 320.

FIGS. 6A and 6B show external views of the upper part 210 of dataacquisition unit 110 according to some embodiments.

Upper part 210 may comprise a charge port 630, as shown in FIG. 6 a .Charge port 630 may be connected or connectable to power source 330.External power sources may connect to charge port 630 in order to chargepower source 330.

Upper part 210 may comprise a debugging port 672. Debugging port 672 maybe communicatively coupled to one or more components on peripheralprinted circuit board 320 and/or printed circuit board 310. Debuggingport 672 may be communicatively coupled to processor 984.

FIG. 6B shows an external view of upper part 210 and the modem receivingfeature 218, which may be formed as a shallow recess, according to someembodiments. The modem receiving feature 218 may be shaped to receive avariety of modems. Referring to FIG. 6B, the modem receiving feature 218can be visibly shown in the middle of top surface 217 of upper part 210.However, in some embodiments, the modem receiving feature 218 may extendto edges of top surface 217, for example as an inlet underneathprotection plate 226, to channel rainwater accumulation from top modemreceiving feature 218.

FIGS. 6C and 6D show cross-sectional views of the upper part 210 of dataacquisition unit 110 according to some embodiments.

Upper part 210 may comprise modem port 690, as shown in FIG. 6 c . Modemport 690 may also be referred to as modem serial port 690, or modemcomms 690. Modem port 690 may be a port for attaching cabled connectionsto connect modem 290 to peripheral printed circuit board 320, printedcircuit board 310, and/or processor 984.

Upper part 210 may comprise water proof O-rings or other sealingcomponents, such as water-proofing O-ring 631, to better seal housing205 from water/debris, as shown in FIG. 6 c.

Upper part 210 may comprise one or more upper part cavities 682, asshown in FIG. 6 d . The one or more upper part cavities 682 may belocated on an underside surface of upper part 210. The one or more upperpart cavities 682 may be recesses in upper part 210 formed to partiallyreceive or accommodate one or more power clamps 434 and/or one or morepower clamp structures 433. Upper part 210 may comprise 2 to 10 upperpart cavities 682. In some embodiments, upper part 210 may comprise 2,3, 4, 5, 6, 7, or 8 upper part cavities. In some embodiments, upper part210 comprises 8 upper part cavities 682.

Upper part 210 may also comprise communications antenna recess 667, asshown in FIG. 6 d . In some embodiments, communications antenna recess667 may be a recess to permit cables to connect from within housing 205,such as from printed circuit board 310 to connect to antenna connector216 and communications antenna 266. In some embodiments, a similarrecess to the recess for communications antenna 266 is used to allowconnections to other components on upper part 210, such as passive GNSSantenna 262.

In some embodiments, each of the one or more integration columns 633 maycomprise a column screw recess 634, as shown in FIG. 6 d . Column screwrecess 634 may be a recess on a surface of integration column 633 whichcan receive housing screw 634 to secure the integration column 633 tobottom part 230.

FIG. 7 is a schematic diagram showing components of the data acquisitionunit 110 according to some embodiments.

According to some embodiments, charge port 630 may be a panel mountableconnector. Charge port 630 may be referred to as battery charge port630. Charge port 630 may be an XLR connector. Charge port 630 may be aSwitchcraft B3MH. Charge port 630 may include a dust cap. The dust capof charge port 630 may be a CPMSB. Charge port 630 may be cableconnected to either printed circuit board 320 or printed circuit board310. As shown in FIG. 7 , charge port 640 is cable connected toperipheral printed circuit board 320.

In some embodiments, debugging port 672 may be a panel mountableconnector. In some embodiments, debugging port 672 is a receptacleconnector. In some embodiments, debugging port 672 is an Amphenol LTWM12A-08PFFS-SF8002 or M12A-12PFFS-SF8002, for example. Debugging port672 may be cable connected to either printed circuit board 320 orprinted circuit board 310. As shown in FIG. 7 , debugging port 672 iscable connected to peripheral printed circuit board 320.

In some embodiments, modem port 690 may be a panel mountable connector.In some embodiments, modem port 690 is a receptacle connector. In someembodiments, modem port 690 is an Amphenol LTW M12A-08PFFP-SF8001. Modemport 630 may be cable connected to either printed circuit board 320 orprinted circuit board 310. As shown in FIG. 7 , modem port 630 is cableconnected to peripheral printed circuit board 320.

In some embodiments, button 214 is a switch button as shown in FIG. 7 .Button 214 may also be referred to as power switch 214. Button 214 maybe an SPST switch. Button 214 may be an SPST JWMW11RA2A switch. In someother embodiments button 214 is a push button. Button 214 may be cableconnected to either printed circuit board 320 or printed circuit board310. As shown in FIG. 7 , button 214 is cable connected to peripheralprinted circuit board 320.

In some embodiments, LED indicator 270 is a multi-colour indicator. Asshown in FIG. 7 , LED indicator 270 is a bi-colour indicator. LEDindicator 270 may be cable connected to either printed circuit board 320or printed circuit board 310. As shown in FIG. 7 , LED indicator 270 iscable connected to peripheral printed circuit board 320. LED indicatormay be an APEM Q8F7BZZRYG02E, for example.

Level indicator 280 may be a bulls-eye indicator. Level indicator 280may be a Spirit Level RS PRO 667-3913, as shown in FIG. 7 .

Communications antenna 266 may be a LoRa antenna, as shown in FIG. 7 .Communications antenna 266 may be a LoRa Antenna ANT-916-CW-HWR-SMA, asshown in FIG. 7 . Communications antenna 266 may be cable connected toeither printed circuit board 320 or printed circuit board 310. As shownin FIG. 7 , communications antenna 266 is cable connected to printedcircuit board 310.

Passive GNSS antenna 262 may be a monopole antenna, such as TS.07.0113,for example. In some other embodiments, device 213 and/or dataacquisition unit 110 includes both active GNSS antenna 264 and passiveGNSS antenna 262. Passive GNSS antenna 262 may be cable connected toeither printed circuit board 320 or printed circuit board 310. As shownin FIG. 7 , passive GNSS antenna 262 is cable connected to printedcircuit board 310. In some other embodiments, data acquisition device213 and/or data acquisition unit 110 does not include passive GNSSantenna 262, but instead includes active GNSS antenna 264. Passive GNSSantenna 262 may be a GPS antenna, as shown in FIG. 7 . Active GNSSantenna 264 may be GPS Antenna MIKROE-363.

Power source 330 may be an encased battery pack, as shown in FIG. 7 ,containing one or more cells. Power source 330 may be a 3S12P Li-Ionbattery pack, as shown in FIG. 7 . In some other embodiments, powersource 330 may be a S316P Li-Ion battery pack. In some embodiments, theselection of power source 330 in data acquisition device 213 may beinfluenced by power requirements of the satellite modem 290. Powersource 330 may be cable connected to either printed circuit board 320 orprinted circuit board 310. As shown in FIG. 7 , power source 330 iscable connected to peripheral printed circuit board 320.

Vibration transducer 350 may be a Seis Tech ST-2A geophone, as shown inFIG. 7 . Vibration transducer 350 may be cable connected to eitherprinted circuit board 320 or printed circuit board 310. As shown in FIG.7 , vibration transducer 350 is cable connected to printed circuit board310.

Data acquisition device 213 may also comprise a circuit boardsconnection 311. Circuit boards connection 311 may provide power and/ordata transmission between components mounted or connected to printedcircuit board 310 and peripheral printed circuit board 320.

Circuit boards connection 311 may comprise one or more cabledconnections 312. Each of one or more cabled connection 312 may be acable assembly. Each of one or more cabled connection 312 may be arectangular cable assembly. Circuit boards connection 311 may compriseone, two, three, or four cabled connections 312. In some embodimentscircuit boards connection 311 comprises two cabled connections 312 a and312 b, as shown in FIG. 7 . In some embodiments two or more cabledconnections may reduce the number of communication lines per cableassembly, thereby better fitting within one or more cable recess 422. Insome embodiments, cabled connections 312 a is a Molex 2147501062. Insome embodiments, cabled connection 312 b is a Molex 2147501082.

Circuit board connections may also comprise one or more peripheral PCBconnection points 313 and one or more lower PCB connection points 314.One or more peripheral PCB connection points 313 and one or more lowerPCB connection points 314 may be headers. One or more peripheral PCBconnection points 313 may be mounted on peripheral printed circuit board320. One or more lower PCB connection points 314 may be mounted onprinted circuit board 310. One or more peripheral PCB connection pointsand one or more lower PCB connection points 314 may both be connected toone or more cabled connections 312 and to components and/or wiresconnected/mounted on printed circuit boards 310 and 320. Circuit boardsconnection 311 may comprise one, two, three, or four peripheral PCBconnection points 313 and lower PCB connection points 314. In someembodiments circuit boards connection 311 comprises two peripheral PCBconnection points 313 a and 313 b, and two lower PCB connection points314 a and 314 b, as shown in FIG. 7 .

FIGS. 8A and 8B show the printed circuit boards of the data acquisitionunit 110 according to some embodiments. Printed circuit board 310 andprinted circuit board 320 may also bear electronic components to eachform a respective printed circuit board assembly.

Printed circuit board 310 may mount inertial measurement unit 950,analogue to digital converter 920, volatile memory 940, processor 984,one or more lower PCB connection points 314, GNSS unit 994, serial unit1474, and power port 835, as shown in FIG. 8A. Power port 835 may allowconnection of external power to power components mounted or connected toprinted circuit board 310.

Peripheral printed circuit board 320 may mount connectors 830, modemconnector 890, led connector 870, one or more peripheral PCB connectionpoints 313, and debugging connector 872. Printed circuit board 320 mayalso comprise a power regulator.

Connectors 830 may provide an interface from cabled connections frompower source 330, button 214, and/or charge port 630 to componentsand/or wires on printed circuit board 320.

Modem connector 890 may provide an interface from cabled connection fromsatellite modem 290 to components and/or wires on printed circuit board320.

LED connector 870 may provide an interface from cabled connection fromLED indicator 280 to components and/or wires on printed circuit board320.

Debugging connector 872 may provide an interface from cabled connectionfrom debugging port 672 to components and/or wires on printed circuitboard 320.

FIGS. 19A and 19B show examples of printed circuit boards 310 and 320according to some other embodiments.

According to some other embodiments, printed circuit board 310 includesa crystal oscillator 1910. Crystal oscillator 1910 may becommunicatively and/or electrically coupled to analogue to digitalconverter 920. Crystal oscillator 1910 may provide a stable clock inputto the ADC 920, at a much higher rate than the ADCs 920 sampling rate.

According to some other embodiments, printed circuit board 320 includesremovable auxiliary memory 1930. Removable auxiliary memory 1930 mayalso be referred to as expandable memory 1930. In some embodiments,removable auxiliary memory 1930 may allow data acquisition unit 110storage for retransmission, back-up and/or recovery. Removable auxiliarymemory 1930 may be an attachable memory source, such as an SD-card orflash memory. In some embodiments, removable auxiliary memory 1930 is amicro-SD card. Removable auxiliary memory 1930 may be housed and/orconnectable in an expandable memory reader mounted on printed circuitboard 320 and/or 310.

Removable auxiliary memory 1930 may be used to store pre-processed dataas it is batched and before it is transmitted via the modem 290.Removable auxiliary memory 1930 may be configured to store no more than2 to 10 days of pre-processed data and/or a full battery charge worth ofdata sampling and transmission.

Processor 984 may store a copy of the pre-processed data in removableauxiliary memory 1930, and maintain pre-processed data as a contingencyin the case that there is a problem with transmitting some or all of thepre-processed data to the satellite 130, backhaul communications, modem290, or server system 150, etc. The pre-processed data can then bedownloaded via the debugging port 872 of the data acquisition unit 110by a user/field operator, for example, when the data acquisition units110 have been collected from the field. Therefore, the storage of copiedpre-processed data in removable auxiliary memory 1930 can aid datarecovery after communication/component failure. In some embodiments,storage of copied pre-processed data can be accessed by processor 984for re-transmission of the pre-processed data after communication and/orcomponent failure.

According to some other embodiments, printed circuit board 320 includesan auxiliary processor 1984. Processor 1984 may form part of processingunit 902. Processor 1984 may be communicatively coupled to processor 984and components on printed circuit board 320, such as removable auxiliarymemory 1930, for example. Processor 1984 may handle communicationsbetween processor 984 (or processing unit 902), modem 290, and removableauxiliary memory 1930, for example. Processor 1984 may also provideadditional processing and/or application software to assist processor984.

According to some other embodiments, printed circuit board 320 includesone or more dual in-line package (DIP) switches 1920. The DIP switches1920 are communicatively coupled to devices, such as communications unit970, processor 1984 and/or processor 984. The DIP switches 1920 may beconfigured and/or configurable to alter the operating state and/orcontrol operation of communications unit, processor 1984 and/orprocessor 984. For example. The DIP switches 1920 may be configured toboot-up communications unit 970, processor 1984 and/or processor 984 ina different mode or configuration without having to reflash a differentfirmware image. In some embodiments, the DIP switches 1920 may beconfigured to be toggleable by a user/field operator to set the LPWANfrequency of communications unit 970 to the required countryconfiguration, such as toggling the communications unit 970 to operatebetween AU915 for Australia or EU868 for Europe, for example.

FIG. 9 is an example block diagram of a data acquisition unit 110according to some embodiments.

Printed circuit board 310 may bear electronic components shown in FIGS.9 and 14 to form a printed circuit board assembly.

The electronic components may comprise a processor 984, an analog todigital converter 920, geolocation unit (e.g. including a GNSS module)994, power source 330, inertial measurement unit 950, components forconnectivity to geophone 350, volatile memory 940, serial module 1474and programmer/debugger unit. Inertial measurement unit 950 may be amicro-electromechanical systems (MEMS) accelerometer. Electroniccomponents may also comprise any other connections or circuit elements,such as diodes, capacitors, inductors, resistors, and transistors.

In some embodiments, processor 984 is a microcontroller. Processor 984forms part of processing unit 902. Processing unit 902 may compriseprinted circuit board 310. Processing unit 902 or processor 984 maycomprise volatile memory 940 and non-volatile memory 930 so that memory940 and 930 are accessible to the microcontroller of processor 984.Processing unit 902 is responsible for controlling operation of the dataacquisition unit 110, most of the work of which is performed byprocessor 984.

Non-volatile memory 930 may comprise operating system code 932.Non-volatile memory 930 may also comprise pre-determined or periodicallydetermined operational parameters and device operation management code934 as described in relation to FIG. 15 . Non-volatile memory 930 mayalso comprise geophone sample handler code 936, as described below inrelation to FIG. 13 .

Volatile memory 940 may comprise a first samples buffer 942, s secondsamples buffer 944, and a payload queue 946, the functions of which arefurther described in FIG. 15 .

In some embodiments, processor 984 is packaged with the datacommunications unit 970 including a chip for long-range wirelesscommunications. In some other embodiments, the data communications unit970 including the chip for long-range wireless communications is notpackaged with processor 984, but instead is another electronic componentwhich interfaces with processor 984 outside of the processor's package.In some embodiments, the data communications unit 970 is a LPWAN unitand the chip for long range wireless communications is an LPWAN chip. Insome embodiments, the LPWAN chip is a LoRaWAN chip which utilises aLoRaWAN protocol. The LoRaWAN chip may be used for low-power consumptionduring transmission, as well as utilising communication rangecapabilities. The data communications unit 970 including the chip forlong range wireless communications enables processor 984 to communicatewith a user device. Data communications unit 970 may communicate viacommunications antenna 266.

GNSS unit 994 may enable processor 984 to communicate with a GNSSsatellite 2010 for receiving positioning and timing data. The GNSSsatellite may be a global positioning system (GPS) satellite, forexample. GNSS unit 994 is communicatively coupled to passive GNSSantenna 262 and/or active GNSS antenna 264 via cabled connections.

Serial module 1474 may enable serial communications between processor984, components within data acquisition unit 110, within dataacquisition device 213, and/or external devices. Serial module 1474 mayenable RS-232 communications via a serial bus, for example. Serialmodule 1474 may enable serial communications between processor 984 andmodem 290, for example.

Power source 330 may supply power to processor 984 and other componentson printed circuit boards 310 and 320. According to some embodiments,power source 330 may also be able to supply power to another externaldevice, or other connected device. For example, the other device may beconnected through a serial connection such as serial connector on dataacquisition device 213.

ADC 920 may be used to convert voltages measured by components such asvibration transducer 350 and output the digital data to processor 984.In some embodiments, ADC 920 amplifies the signal using an in-builtprogrammable gain amplifier (PGA) prior to outputting the digital datato processor 984. The ADC 920 in some embodiments is used with avibration transducer to measure differential voltage proportional to theinduced velocity.

In some embodiments, the electronic components are chosen for theirlow-power consumption and capability. Components may be chosen optimalto the design rather than being limited to commercial modules. Inaddition, the PCBA may be designed to consume as little power aspossible to extend its battery life in the field.

Programmer/debugger unit may be implemented in hardware and/or softwareto assist analysis of errors in components and/or subsystems of dataacquisition unit 110, such as processor 984. A programmer/debugger unitmay be communicatively coupled to processor 984 and/or serial module1474. In some embodiments, data acquisition unit does not comprise aprogrammer/debugger unit, but instead comprises external portconnections, such as debugging port 672 and debugging connector 872, sothat an external devices can communicate with processor 984 and performprogramming and/or debugging functions.

FIG. 10 shows a flow diagram of a method of sampling by data acquisitionunit 110 according to some embodiments.

In method 1000, data is sampled from the signal output of the vibrationtransducer 350 by the ADC 920 and then written into a first buffer atstep 1002. If processor 984 detects the buffer has become full at step1004, processor 984 batch pre-processes the first buffer with method1200 whilst continuing to sample into the second buffer at step 1006. Ifprocessor 984 detects that the second buffer is full at step 1008,processor 984 batch pre-processes the second buffer with method 1200whilst continuing to sample into the first buffer at step 1002.

FIG. 11 shows a flow diagram of a method 1100 of sampling by dataacquisition unit 110 according to some other embodiments. Method 1100 issimilar to method 1000, except processor 984 performing method 1100 maystop sampling a buffer and shift sampling to another buffer upon anepoch alignment or synchronisation event, for synchronising with otherseismic data acquisition units 110 in array 115. In some embodiments, anepoch alignment or synchronisation event is periodic. In someembodiments, periodic epoch alignment events may be performed at aninterval of 15 minutes, 30 minutes, 1 hour, or 2 hours, for example.

FIG. 17 shows a flow diagram of a method 1700 of sampling by dataacquisition unit 110 according to some other embodiments. Method 1700 issimilar to method 1000 and method 1100, as it includes steps 1002, 1004,1200, 1006, 1008, and 1200, except the processor 984 performing method1700 may stop sampling a buffer and rewrite/re-sample on the same bufferwhen a time synchronisation event is scheduled to commence at that time.Therefore, buffered data may be lost in performing the steps of method1700. For example, processor 984 may check if there is a timesynchronisation event scheduled to commence at that time at steps 1710and 1712. If there is a time synchronisation event scheduled to commenceat that point in time at step 1710 or 1712, processor 984 may then set anext sample buffer index to the beginning of the same buffer at steps1714 or 1712 respectively. If there is a time synchronisation eventscheduled to commence at that point in time at step 1710 or 1712,processor 984 will continue to sample data in the same buffer at thenext buffer index at steps 1002 or 1006 respectively. In someembodiments, a time synchronisation event may occur at an interval of 1minute, 5 minutes, 10 minutes, 15 minutes, 30 minutes, 1 hour, or 2hours, for example.

FIG. 12 shows a flow diagram of a method 1200 of pre-processing of thesampled data by the processor 984 of data acquisition unit 110 accordingto some embodiments.

The method 1200 may condition the data collected from the geophone 350and/or ADC 920 at method 1000 or 1100 for seismic analysis and to reducethe data size significantly. In some embodiments, processor 984 mayrequire a lower sampling rate than ADC 920. For example ADC 920 maysample at 100 Hz but processor 984 may only sample at 25 Hz. Hence, at afirst stage decimation at step 1205 may be required prior to detrendingat step 1210. Therefore, before step 1210, method 1200 may begin withapplication of finite impulse response (FIR) filter on the sampled datafrom ADC 920. The FIR filter may be a low-pass filter to mitigatealiasing of the data prior to pre-processing. In some embodiments, theADC may intrinsically sample at a high rate, for example 100 Hz, butalso is configured to down-sample/decimate the samples to a lower rate,for example 25 Hz. In some embodiments, an RC filter is used betweengeophone 350 and ADC 920 to mitigate noise and aliasing. In some otherembodiments, if ADC 920 does not support a desired lower sampling rate,for example 20 Hz, processor 984 may perform down-sampling/decimation.

Then processor 984 may decimate the data (i.e. by a factor of 4, for theabove example sampling frequencies) before commencing step 1210. Thedecimation may be performed by a pre-determined factor that depends onthe sampling rate. For example, the decimation factor may be two whenthe sampling rate is 50 Hz. In some embodiments, decimating at step 1210may be optional and dependent upon the selected sampling rate. Thesecond stage de-trends or de-biases the sampled data at step 1205. Thisis intended to remove inherent biases in the geophone signal (such as aDC bias or temperature influence). The third stage uses a fast Fouriertransform (FFT) algorithm to convert the time-domain seismic signal intoits frequency constituents at step 1212. This algorithm requires thedata buffer size to be an exponent factor of two. With the data in thefrequency domain, the signal can be filtered by applying pre-determinedfilter coefficients or making changes to the amplitude and frequencybins at step 1215. A low pass filter may be implemented on thede-trended or decimated data after FFT at step 1215. As such, the fourthstage of method 1200 spectrally whitens the frequency domain data atstep 1220. By whitening the data, the amplitude across a frequency rangemay be normalised with a window function. The window function may haverounded edges, such as a Tukey window. The rounded edges of a Tukeywindow are intended to reduce any aliasing (artefacts) when transformingthe data back into the time domain. The fifth stage then transforms thespectrally whitened data by using the inverse fast Fourier transform(IFFT) algorithm at step 1222. The sixth and final stage of thisprocessing pipeline one-bit normalises the data at step 1225. Amplitudesthat are positive are represented with a one, and contrariwiseamplitudes that are negative are represented with a zero. Even thoughthe amplitude information of the original seismic signal is essentiallyobliterated, the phase information of the signal is preserved. This iscritical to the cloud processing side where the data is used to generate3-D sub-surface models.

The one-bit normalisation compresses the data substantially, allowingthe original four-byte sample (from a 32-bit analogue to digitalconverter) to be represented by a single bit. From the perspective ofthe payload that can be sent via the satellite modem, each byte willcontain eight samples. This compression has significant advantages forthe high power demands of satellite backhaul communications.

The one-bit normalised data is then processed into a payload at step1230.

The payloads are sent to modem 290 for scheduled transmission at step1235. In some embodiments, the payloads are first batched locally onvolatile memory 940 before being sent to modem 290 at step 1235. In someembodiments, the payloads are first batched on removable auxiliarymemory 1930 before being sent to modem 290 at step 1235. In someembodiments, the payloads are transmitted in a scheduled transmissiontime period with a randomised transmission time. The randomisedtransmission time may be determined using a unique identifier, such as ahardware serial number from the processor 984, as a randomisation key,for example. In some embodiments, the payloads are sent by processor 984to modem 290 at a randomised time using the unique hardware serialnumber from the processor 984 as a key, then enabling modem 290 toperform the scheduled transmission. This may allow a plurality of nearbydata acquisition units 110 to avoid interference with each other fortheir scheduled uplink transmissions, particularly when the dataacquisition units 110 of data acquisition array 115 are synchronisedwith their respective seismic data sampling.

FIG. 13 shows a flow diagram of a method 1300 of sampling andpre-processing by the data acquisition unit 110 according to someembodiments.

As mentioned with regards to method 1000, data is sampled and stored ina buffer before being pushed through a sequence of processing algorithmsas described in method 1200. At the beginning of method 1300, the datafrom sensed vibrations may be sampled at step 1310. At step 1320, thesampled data may then be transmitted to an analogue to digital converter920 and each sample is converted into a 32-bit float number, and thatnumber is sent to a sample buffer. Steps 1310 and 1320 combined aresimilar or equivalent to steps 1002 or 1006 of method 1000 of FIG. 10 .The sample buffer may hold 512 samples, for example. In some otherembodiments, the sample buffers may hold 64, 128, 256, or 1024 samples,for example. Once the sample buffer is full, method 1300 may continuewith the execution of ambient noise processing at step 1312. Thoseprocessing algorithms for executing ambient noise processing at step1312 may include steps 1205, 1210, 1212, 1215, 1220, 1222, and/or 1225shown and described in relation to FIG. 12 , for example.

Once the processed data is ready, it is batched into the payload thatwill be transmitted. In some embodiments, the data is transmitted on apayload of 240 or more bytes from the processor 984 to modem 290. Insome embodiments, some additional flash memory may be added to theprinted circuit board 310. The intent is to concatenate pre-processeddata batches with this local memory into one large payload over time.Once filled, the payload will be sent to the modem 290 for transmissionto a satellite 130 during overpass. This is advantageous becausetransmitting fewer, larger payloads with the modem is morepower-efficient than sending many smaller payloads.

Timing is relevant to the ambient noise tomography technique. The GNSSmodule 994 may provide a synchronisation payload to processing unit 902at boot or at a predetermined timing, for example every 4 hours, 2hours, 1 hour, 30 minutes, 10 minutes, or 1 minute. To keep precisetiming, a pulse per second (PPS) signal generated from the GNSS module994 may be used to drive the on-board system clock of processor 984.This pulse is synchronous across each GNSS module 994 of dataacquisition units 110 and data acquisition devices 213 of dataacquisition array 115 with a satellite fix. Instruments deployed in thefield are intended to be synchronised and to maintain their timing withthe same PPS signal. A separate hardware timer inside processing unit902 can be used to generate an interrupt service routine (ISR) andsample the geophone. If the sample rate is 25 Hz, 25 samples areexpected to be collected within one cycle of the PPS. If there are anylatency issues with the timing, then the PPS can correct the timer. Asshown at step 1310, the processor 984 executing geophone sampler 936 mayperform the interrupt service routine to sample every 25th sample,triggered by the hardware timer interrupt.

In some other embodiments, the hardware timer inside processing unit 902drives the milliseconds of the on-board clock. In some otherembodiments, sampling of the geophones is driven by the ADC 920. ADC 920then can signal to processing unit 902 when a sample is ready to bestored in the sample buffer 942 or 944. If the ADC 920 drives thesampling, there is no need to use the PPS to align the sampling buffer.The ADC 920 sampling is synchronised every five minutes by a signal sentfrom processing unit 902 based on a software timer executed by processor902. In some other embodiments, at step 1310, the ADC 920 can signal toprocessing unit 902 when a sample is ready to be stored in the samplebuffer 942 or 944, at a sampling rate of 25 Hz. The ADC 920 may beprovided a highly stable and consistent clock source by crystaloscillator 1910, to assist driving the sampling of the ADC 920.

The sampling rate may be 25 Hz according to some embodiments. In someembodiments, the sample rate may be between 10 Hz to 20 Hz, 15 Hz to 30Hz, or 20 Hz to 40 Hz. In some embodiments, the sampling rate may beabout 5 Hz, 10 Hz, 15 Hz, 20 Hz, 30 Hz, 40 Hz, 50 Hz, or 100 Hz, forexample.

Once the ambient noise processing is executed at step 1312, the 512samples (now each represented by a bit) are processed into a 64 bytearray, and then placed into a communications buffer at step 1230. Thecommunications buffer may be 240 bytes, for example. Communicationsbuffer may be between 120 to 6400 bytes, for example. In some otherembodiments the communications buffer may be about 150 bytes, 300 bytes,480 bytes, 1200 bytes, 2400 bytes, 3600 bytes, or 6400 bytes forexample.

If the communications buffer has less than 64 bytes remaining at step1327 processor 984 may then send the data in the communications bufferto the satellite modem 290 at step 1235.

FIG. 14 shows a schematic diagram of electronic components of the dataacquisition unit 110 according to some embodiments.

As described above, the electronic components of data acquisition device213 may include analogue to digital converter 920, vibration transducer350, processor 984, serial module 1474, volatile memory 940, inertialmeasurement unit 950, GNSS unit 994, power source 330, and lower PCBconnection points 314, as shown in FIG. 14 .

Inertial measurement unit 950 may be used to determine the orientationand/or the attitude of the data acquisition unit 110 and dataacquisition device 213 after it is deployed. The orientation measured byinertial measurement unit 950 can be signalled to processing unit 902.Processing unit 902 can then send the orientation information reportingas a part of a health data payload in a signal to be transmitted bymodem 290 over satellite to be received by server system 150 and thenvisualised on a user device, for example, client device 160. In someother embodiments, processing unit 902 can send the health data payloadLPWAN communications, via data communications unit 970 andcommunications antenna 266, to a technician in the field. If theorientation of the data acquisition unit 110 and/or data acquisitiondevice 213 has been manipulated at any time due to external disturbances(wind, rain, animals, etc.) then it will impact the sensitivity of thegeophone 350 and thus the data quality. This allows a user/technician togo out and resolve the problem only when needed, mitigating the risksand costs of having somebody in the field manually inspecting the dataacquisition units 110. In some embodiments, server system 150 isconfigured to transmit to client device 160 a current and/or historicalmeasurement of the attitude or orientation of data acquisition unit 110based on a determination of one or more health data payloads receivedfrom data acquisition unit 110. In some embodiments, server system 150is configured to transmit to client device 160 an alert to client device160 indicating a change of the attitude or orientation and/or an amountof change of the attitude or orientation of data acquisition unit 110 toa previous attitude or orientation of the data acquisition unit 110,based on a determination from two or more health data payloads receivedfrom data acquisition unit 110.

FIGS. 20A and 20B show schematic diagrams of electronic components ofthe data acquisition unit 110 according to some other embodiments.

As described above, the electronic components of data acquisition device213 may include ADC 920, vibration transducer 350, processor 984, serialmodule 1474, volatile memory 940, inertial measurement unit 950, GNSSunit 994, power source 330, and lower PCB connection points 314, asshown in FIG. 14 .

In some embodiments, the electronic components of data acquisitiondevice 213 also include inertial measurement unit 950, DIP switches1920, LED connector 870, debugging connector 872, processor 1984,removable auxiliary memory 1930, modem connector 890, peripheral PCBconnection point 313, and connectors 830.

FIGS. 15A, 15B, 15C, and 16 show some example 3-D sub-surface imagingaccording to some embodiments. The sub-surface imaging may be throughambient noise tomography processing.

Sub-surface imaging may be performed by server system 150 upon receivingpreprocessed data of method 1200 from one or more data acquisition units110 of data acquisition array 135. Representations and modelling of thisimaging may be viewable on client computing device 160.

FIG. 15A shows a gravity method survey yielding a false positive result.This is in contrast to an ambient noise tomography method of FIG. 15Bover the same sub-surface yielding a correct determination of anomalies.FIG. 15B is an example two-dimensional (2-D) splice of a 3-D model. Useof ambient noise techniques may allow dense bodies (typical sources ofiron oxide copper-gold, or lithium, for example) to be identified.

In some embodiments, the data acquisition units 110 of data acquisitionarray 115 may be deployed in different configurations. In someembodiments, the survey area for imaging may be dependent upon theboundary defined by a perimeter of data acquisition units 110 of thedata acquisition array 115. In some embodiments, the data acquisitionunits may be deployed in an evenly spaced rectangular formation with theimaging area a perimeter boundary defined by the outside dataacquisition units 110. In some other embodiments, the data acquisitionunits 110 of data acquisition array 115 are not all evenly spaced fromone another. In some other embodiments, the data acquisition units 110of data acquisition array 115 are not deployed in a rectangularformation but another arrangement.

In some embodiments, data acquisition units 110 of data acquisitionarray 115 may be deployed at an equal or near equal distance from oneanother. In some embodiments, data acquisition units 110 may be deployedat a distance of about 20 metres to about 2 kilometres. In someembodiments, data acquisition units 110 may be deployed at a distance ofabout 30 metres to about 100 metres, about 100 metres to about 500metres, or 500 metres to about 1.5 kilometres, for example. In someembodiments, data acquisition units 110 may be deployed at a distance ofabout 20 metres, 50 metres, 100 metres, 200 metres, 400 metres, 600metres, 800 metres, 1 kilometre, 1.2 kilometres, 1.5 kilometres, orabout 2 kilometres from one another, for example.

The spacing of the deployed data acquisition units 110 in dataacquisition array 115 may influence the depth of imaging. The depth ofimaging may be proportional to the spacing distance of the dataacquisition units 110 of data acquisition array 115. In someembodiments, the depth of imaging may be about 5 times the spacingdistance between each of the data acquisition units 110 of dataacquisition array 115. The greater the spacing distance between dataacquisition units 110 of data acquisition array, the greater the depthof the imaging. However, a greater spacing may lead to a decrease inimage resolution.

In some embodiments, an adequate amount of ground-movement data from oneor more data acquisition units 110 of data acquisition array 115 may becollected for server system 150 to generate a display of a first groundregion on the user interface, and then at least one of the plurality ofdata acquisition units 110 may be repositioned at surface locationsacross a second ground region. Then at least one of the plurality ofdata acquisition units 110 is configured to collect a second amount ofground-movement data for a display of the second ground region beforethe power source 330 or supply requires recharging or replacing.

In some embodiments, the second amount of ground-movement data is anadequate amount of data collected for server system 150 to generate adisplay of the second ground region on the user interface.

In some embodiments, the data acquisition units 110 are repositionedfrom the first ground region to the second ground region via at least inpart by vehicular transport.

In some embodiments, a further one or more data acquisition units 110are deployed in the first ground region whilst server system 150 isreceiving pre-processed ground movement data and/or performing ambientnoise tomography and/or generating tomography data and/or generating thedisplay. The server system 150 is then configured to receive and processfurther pre-processed ground movement data from the further dataacquisition units 110 and perform ambient noise tomography and generatetomography data based on both the pre-processed ground movement data andthe further pre-processed ground movement data. In some embodiments, oneor more data acquisition units 110 of data acquisition array 115 in thefirst ground region are moved to another location within the firstground region whilst sampling is occurring, and the server system 150 isthen configured to receive and process the new pre-processed groundmovement data from the repositioned data acquisition units 110 and thestagnant data acquisition units 110 and perform ambient noise tomographyand generate tomography data from the data sampled from the dataacquisition array 115.

Parts List 100 Sub-surface Tomography System 110 Data acquisition unit115 Data acquisition array 118 Satellite communication link 130 LEOSatellite 135 Satellite Constellation 138 Ground station communicationslink 140 Ground Stations 148 Server system communications link 150Server System 152 Data storage 154 Tomography module 156 Datavisualisation module 157 Client device communications link 160 Clientcomputing device 205 Housing 213 Data acquisition device 210 Upper part211 Side panel 214 Button 216 Antenna connector 217 Top surface of upperpart 218 Modem receiving feature 220 Modem cap 226 Protection plate 230Bottom part 250 Sensing probe 251 Distal tip 252 Probe recess 262Passive GNSS antenna 264 Active GNSS antenna 266 Communications antenna270 LED indicator 280 Level indicator 290 Satellite Module 310 Printedcircuit board 311 Circuit boards connection  312a Cabled connection 312b Cabled connection  313a Peripheral PCB connection point  313bPeripheral PCB connection point  314a Lower PCB connection point  314bLower PCB connection point 320 Peripheral printed circuit board 330Power source 333 Integration column 334 Housing screw 336 Tool recess338 Column receiving recess 350 Vibration transducer or ground sensingmodule 352 Probe gasket 354 Probe receiving recess 355 Probe buttress356 Probe connection gasket 362 Top portion 364 Central portion 366Bottom portion 420 Internal floor of bottom part 422 Cable recess 430Enclosed wall 431 Inner surface of enclosed wall 432 Connection rim 433Clamp structure 434 Power source clamp 435 Power source positioningbracket 436 Clamp screw recess 437 Cable guide 440 Column mountingportions 630 Charge port 631 Water proof O-ring 672 Debugging port 690Modem port 634 Column screw recess 667 Communications antenna recess 682Upper part cavities 830 Connectors 835 Power port 870 Led connector 872Debugging connector 890 Modem connector 902 Processing unit 984Processor 930 Non-volatile memory 932 OS code 934 System tick handler936 Geophone sampler 938 Preprocessor code 940 Volatile memory 942 Firstsamples buffer 944 Second samples buffer 948 Payload queue 994 GNSS unit950 Inertial measurement unit 920 Analogue to digital converter 910 GNSSsatellite 1474  Serial module 1810  Handle 1812  Handle ends 1910 Crystal oscillator 1920  DIP switches 1930  Removable auxiliary memory1984  Processor 2133  Clamping sheet 2250  Engagement projection

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the above-describedembodiments, without departing from the broad general scope of thepresent disclosure. The present embodiments are, therefore, to beconsidered in all respects as illustrative and not restrictive.

1. A data acquisition unit, including: a housing; a ground movement dataacquisition mechanism configured to measure ground movement; aprocessing unit communicatively coupled to the ground movement dataacquisition mechanism, wherein the processing unit is configured toreceive ground movement data sent from the ground movement dataacquisition mechanism, the processing unit further configured topre-process the ground movement data before transmitting, via asatellite modem, to a communicatively coupled LEO satellite thepre-processed data based on a scheduled timing of the LEO satellitereaching a scheduled orbital position.
 2. The data acquisition unit ofclaim 1, wherein the ground movement data acquisition mechanism andprocessing unit continuously acquire and pre-process ground movementdata and transmit all or almost all the pre-processed data to a remoteserver system via the low earth orbit satellite for performing ANT. 3.The data acquisition unit of claim 1, wherein pre-processing the groundmovement data includes one-bit normalisation.
 4. The data acquisitionunit of claim 1, wherein pre-processing the ground movement data furtherincludes detrending the ground movement data.
 5. The data acquisitionunit of claim 1, wherein pre-processing the ground movement data furtherincludes low-pass filtering.
 6. The data acquisition unit of claim 1,wherein pre-processing the ground movement data further includesdecimating by a pre-determined factor that depends on a data samplingrate.
 7. The data acquisition unit of claim 1, wherein pre-processingthe ground movement data further includes spectral whitening.
 8. Thedata acquisition unit of claim 1, wherein pre-processing the groundmovement data further includes: detrending performed first, followed bydecimating by a pre-determined factor, followed by low-pass filtering,followed by spectral whitening, followed by one-bit normalisation.
 9. Adata acquisition unit for ambient noise tomography (ANT), including: aclosed housing including a top portion, a central portion and a lowerportion, the lower portion including a vibration sensing portion forsensing vibration in a ground region; a vibration transducer in thehousing and configured to receive vibrations via the vibration sensingportion and generate an electrical output signal based on the receivedvibrations: a processing unit in the housing to receive and process theelectrical output signal to generate a compressed data payload; asynchronisation unit to receive a synchronisation signal from asatellite and to communicate synchronisation data to the processing unitbased on the synchronisation signal; a satellite modem communicationport positioned on top of the top portion for allowing communicationbetween a satellite modem and the processing unit to transmit the datapayload to a low earth orbit satellite; and a power supply in thecentral portion to supply power to the processing unit, the satellitemodem and the synchronisation unit.
 10. The data acquisition unit ofclaim 9, wherein the vibration transducer includes a geophone positionedin the vibration sensing unit.
 11. The data acquisition unit of claim10, wherein the vibration sensing unit includes a metal spike or probehaving one end received in the lower portion and a free opposite end forextending into part of the ground region.
 12. The data acquisition unitof claim 11, wherein the power supply includes a rechargeable batterymodule centrally positioned within the housing.
 13. The data acquisitionunit of claim 12, wherein the processing unit is disposed between thepower supply and the sensing probe, vibration transducer, or thevibration sensing portion.
 14. The data acquisition unit of claim 13,further including a low-power wide-area network (LPWAN) antennaconnection jack in a top portion of the housing for coupling a LPWANantenna to the processing unit.
 15. The data acquisition unit of claim9, wherein the processing unit is configured to buffer payload data fora pre-determined period of time less than 12 hours.
 16. The dataacquisition unit of claim 9, wherein the satellite modem is configuredto transmit the data payload to a remote server in near-real time. 17.The data acquisition unit of claim 9, wherein the processing unit sendsthe data payload at a randomised time within a scheduled transmissionperiod.
 18. The data acquisition unit of claim 9, further comprising aninertial measurement unit for measuring an attitude and/or orientationof the data acquisition unit, wherein the processing unit batches theattitude and/or orientation data in a payload for transmission so thatthe attitude and/or orientation, or a change of attitude and/ororientation, of the data acquisition unit, can be visualised on oralarmed to a user device.
 19. The data acquisition unit of claim 9,further comprising a removable auxiliary memory for storing the datapayload for data recovery or re-transmission of one or more of the datapayloads upon communication and/or component failure.
 20. A method ofseismic data acquisition, including: positioning a plurality of the dataacquisition units of claim 1 at spaced surface locations across a groundregion; and operating each of the plurality of data acquisition units toreceive vibrations over a plurality of days; wherein the plurality ofdata acquisition units are operable to generate and send to a satelliteprocessed data based on vibrations received by the data acquisitionunits at the spaced surface locations.
 21. The method of claim 20,wherein the operating includes continuous operation of the dataacquisition units to receive vibrations.
 22. The method of claim 21,wherein the operating includes continuous operation of the dataacquisition units to receive vibrations for a period of between 4 and 10days, wherein a power supply or power source of each data acquisitionunit is contained within the housing of each data acquisition unit andis configured to supply power for operation of the respective dataacquisition unit for more than 10 days.
 23. A server system, including:a data communications module for receiving from a plurality of dataacquisition units pre-processed ground movement data based on groundmovement in a ground region sensed by each of the plurality of dataacquisition units; a data processing module for performing ambient noisetomography to generate tomography data based on the ground-movementdata; and a data visualisation module for generating a display of theground region based on the tomography data viewable from acommunicatively coupled user interface in near-real time relative to adata acquisition time of the ground movement.
 24. The server system ofclaim 23, wherein the pre-processed ground movement data is receivedfrom the data acquisition unit via communications of a low earth orbitsatellite.